1. Field of Art
This invention relates to the improvement of an agricultural tractor. More specifically it relates to an improvement of the hydrostatic transmission.
2. Description of Prior Art
Agricultural tractors have been used for a variety of farming operations for decades. Tractors have become more versatile and are now being used for a greater number of agricultural tasks. More recently the use of a hydrostatic transmission has been used to propel the farm tractor. A hydrostatic transmission is simpler to operate. Instead of having to constantly depress a clutch to change the gears of a transmission, a hydrostatic transmission can be operated by depressing a pedal which controls a pump, which in turn controls a motor. One of the problems with a hydrostatic transmission is the risk that the operator will inadvertently leave the pedal slightly depressed and exit the tractor. The slightest movement of the pedal will result in the tractor `creeping` and possibly injuring an individual. Another problem with the hydrostatic transmission involves the use of two pedals to control the motion of the tractor. Typically, there is a pedal for forward motion and a separate pedal for rearward motion. For some farm operations, such a those requiring a bucket or lift, an operator may be changing directions frequently. The constant alternating between the forward and reverse pedals is tiring to an operator.
The prior art illustrates these and additional difficulties. U.S. Pat. No. 4,759,417 discloses a system and method for controlling the ground speed and enhancing the maneuverability of an off-road vehicle. This patent uses two pedals 116 and 118 to control the speed and direction of the tractor. To prevent the tractor transmission from inadvertently remaining engaged, a complex series of springs adjust to maintain the tractor transmission in neutral. Because the transmission is sensitive to the slightest pedal depression, a grooved cam 74 is used to keep the transmission in precise adjustment. This design also results in the pedal quickly returning to neutral when the pedal is not depressed. This results in an abrupt stop causing the operator some discomfort. The quick motion of the pedal can also create an harmonic vibration which can potentially damage various tractor components. It is also necessary to dampen the motion of the pedal to limit the vibration caused by the tractor engine. This results in additional springs and rods adding cost and complexity to this design.
Consequently, the need exists for a self-centering hydrostatic transmission linkage which minimizes the number of parts and complexity of the transmission system. It would also be advantageous for a single pedal which can control the motion of an agricultural tractor.